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New mount for stirling motors and satalite dish solar and the liquid piston tracker

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Posted by brian white on March 19, 2010, 2:09 am
 
Basically equatorial mount is just constant speed movement on an axis
that is in line with the earth's axis of rotation.  Solar concentrators
on equatorial mount suffer a major problem with seasonal adjustment.
They throw the center of gravity completely out of whack as you move
them up or down to follow the sun higher and lower in the sky. This
makes it much harder to turn the mount too.
The solution might be to put 2 dishes on the axis with a focus at each
end of the axis.  As you move one dish up to follow the sun, you are
moving the other dish down.  The movement of one dish exactly
counteracts the movement of the other one so the center of gravity stays
in the same place all year.
The liquid piston tracker is a bit of an advance on the clock based tracker.
You can see it all at  
There are 2 other videos that go into explaining what equatorial mount
is and  using equatorial mount for solar panels, etc.  The linked video
assumes that you know what equatorial mount is.
Thanks
  Brian

Posted by dow on March 20, 2010, 3:30 pm
 

I love your hydraulic clock power amplifiers. I remember seeing one in
another thing of yours. I forget which one.

I see your point about moving one dish up and the other down, but it's
not obvious to me that the effects on the centre of gravity will
exactly cancel out. Certainly, this will be true in the symmetrical
case that occurs at each equinox (e.g. today!), but far from an
equinox I suspect that one dish's centre of gravity will move faster
than the other, so the overall centre of gravity will not remain on
the polar axis.

Why not use just one dish and attach arms to it with counter-weights
at their ends? Arrange for the centre of gravity of the dish-weight
assembly to coincide with the focus of the dish, and make both axes
(the polar one and the perpendicular one for the seasonal declination
movements) pass through this same focal point. This will make the
assembly balanced about both axes, so very small forces will be
sufficient to turn it.

If you're planning to use a satellite dish, one of the ones that many
people have attached to their houses to receive satellite TV, you'll
have to take account of the fact that these dishes are off-axis
sections of paraboloids. The vertex of the paraboloid, where its
curvature is greatest, is not at the centre of the dish. In fact, it
is usually not part of the dish at all, but is some distance below the
bottom edge. The axis of the paraboloid, which you will want to aim at
the sun, is the line that passes through this vertex and through the
focus, which is where the microwave receiving module is located. The
dishes are designed this way so that the microwave module does not
cast a "shadow" onto the dish, and also so that the dish can be
roughly vertical even though its axis is aimed fairly steeply upward
at the satellite. Having the dish vertical avoids problems with rain
and snow. For your purpose, the off-axis shape of the dish means that
your cooking pot will not cast a shadow onto the dish, which is good.

Fun stuff!

        dow



Posted by dow on March 20, 2010, 8:18 pm
 It occurred to me that if a symmetrical paraboloidal bowl is made of
material of uniform thickness and has some certain depth, relative to
its focal length, then its centre of gravity will be located at its
focus. I tried to calculate the required depth, which turned out to be
much more difficult than I had anticipated. I did eventually get an
answer, which looks reasonable, but I am not 100 percent confident in
it. This answer is that the depth should be 1.8478 times the focal
length. If anyone here can confirm this, I'd be grateful.

If this result is correct, then if you make a paraboloidal bowl out of
metal with uniform thickness, and give it a focal length of 50 cm, for
example, and make the vertical depth of the bowl from the bottom (the
vertex of the paraboloid) to the horizontal rim, 92.39 cm, then the
focus of the bowl will also be its centre of gravity. If you mount
this bowl on any axis that passes through the focus, the bowl will be
balanced so it can be rotated about the axis with very little force.

Of course, if these bowls turn out to be useful, they could be stamped
out in factories in huge numbers very cheaply.

Is this any use to you?

                          dow

Posted by brian white on March 21, 2010, 2:45 am
   Thanks David!
I think that you are the second person genuinely interested in this.
(Other than me)    I was influenced by stuff I read about scheffler
solar kitchens and by my own experience a few years ago when i tried to
make a tracking solar accumulator. I made an off center paraboloid in
late march. Did not think of center of gravity too much! As the season
changed, I moved it to adjust for the changing sun angle and had a devil
of a job keeping the center of gravity close to the axis.

I think that if you have a symmetrical paraboloidal bowl you might end
up having problems supporting the heat collector at certain times of the
year. (I could be wrong on this, of course), perhaps you could cut a
strip out of the bowl where it comes close to the support for the axis?
with the seasonal movement.
Thank you for taking the time to calculate the depth of bowl needed to
have the center of gravity on the axis. That is useful.
I also like the idea that once we get the bowls right they can be
stamped  out in large numbers very cheaply.
I cannot work on any of this anymore. I took time off to "concentrate my
thoughts" which worked but which did negative things to my bank balance.
Thank you
Brian
dow wrote:


Posted by brian white on March 21, 2010, 2:50 am
   Thanks David!
I think that you are the second person genuinely interested in this.
(Other than me)    I was influenced by stuff I read about scheffler
solar kitchens and by my own experience a few years ago when i tried to
make a tracking solar accumulator. I made an off center paraboloid in
late march. Did not think of center of gravity too much! As the season
changed, I moved it to adjust for the changing sun angle and had a devil
of a job keeping the center of gravity close to the axis.

I think that if you have a symmetrical paraboloidal bowl you might end
up having problems supporting the heat collector at certain times of the
year. (I could be wrong on this, of course), perhaps you could cut a
strip out of the bowl where it comes close to the support for the axis?
with the seasonal movement.
Thank you for taking the time to calculate the depth of bowl needed to
have the center of gravity on the axis. That is useful.
I also like the idea that once we get the bowls right they can be
stamped  out in large numbers very cheaply.
I cannot work on any of this anymore. I took time off to "concentrate my
thoughts" which worked but which did negative things to my bank balance.
Thank you
Brian
dow wrote:


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